Excitation and emission properties of inorganic phosphors are mainly determined by host materials, activators, and other dopants. Phosphors composed of different host materials, activators or other dopants may have different luminescent properties, such that the composition is the most important factor in tuning the optoelectronic properties of the phosphors. Mainstream host materials of inorganic phosphors are sulfides, oxides, oxysulfides, or other complex oxides such as silicates, aluminates, phosphates, and the likes. Recently, phosphor development of host materials has partly moved in the direction of nitrides and oxynitrides. The major activators being used are ions of transition-metal elements or rare-earth elements.
Future, light sources should meet the environmental protection requirement of being mercury-less or mercury-free, such that a high-efficiency Xe2* excimer lamp will possibly become a mainstream light source in the future. The Xe2* excimer lamp should probably collocate with a phosphor to convert light from short-wavelength to long-wavelength. For example, the Xe2* excimer lamp emits a vacuum ultraviolet (VUV) light having a wavelength of 172 nm, which can be converted by an appropriate phosphor to emit a UV-B light having a wavelength of 280 to 320 nm or a UV-C light having a wavelength of 200 nm to 280 nm. The UV-B light can be applied in phototherapy such as treating skin diseases such as psoriasis, vitiligo, atopic dermatitis, and the likes. The UV-C light may be applied in disinfection, purification, TOC (total organic compounds) reduction, and the likes. Conventional phosphors excitable by the VUV light from the Xe2* excimer lamp are rare, such that developments of novel phosphors are still called for.